SPC AC 191954
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0254 PM CDT SAT MAY 19 2007
VALID 192000Z - 201200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS CENTRAL/EASTERN MT AND
NORTHEAST WY...
...MT...
SWLY MID LEVEL FLOW EXTENDING FROM ID INTO WRN/CENTRAL MT WILL
CONTINUE TO STRENGTHEN FROM 40-50 KT THROUGH TONIGHT AS THE UPSTREAM
MID/UPPER LEVEL TROUGH SHIFTS INLAND ACROSS THE PACIFIC NW. WATER
VAPOR IMAGERY SHOWED THE LEADING EDGE OF A SHORT WAVE TROUGH
TRACKING NEWD ACROSS WRN MT/SRN ALBERTA EARLY THIS AFTERNOON.
ASCENT WITH THIS FEATURE LIKELY AIDED TSTMS THAT OCCURRED OVER WRN
MT THIS MORNING...WITH MORE RECENT ACTIVITY NOW INTO SRN ALBERTA.
THE SRN EXTENT OF THIS IMPULSE IS EXPECTED TO SPREAD NEWD INTO MT
THIS AFTERNOON AND TONIGHT PROVIDING ASCENT FOR UPWARD VERTICAL
MOTION AND ADDITIONAL TSTMS. SATELLITE IMAGERY/LIGHTNING DATA
INDICATED THAT THIS ASCENT COMBINED WITH SURFACE HEATING IS AIDING
AN INCREASE IN TSTMS ACROSS NWRN WY...WITH ADDITIONAL DEVELOPMENT
OCCURRING INTO SWRN MT. EARLY AFTERNOON SURFACE ANALYSIS SHOWED A
BOUNDARY EXTENDING FROM SWRN SD WNWWD THROUGH SRN MT AND THEN NWWD
INTO WRN MT. A NARROW AXIS OF SURFACE DEWPOINTS IN THE LOWER 50S
ALONG THIS BOUNDARY AND BENEATH STEEP LAPSE RATES ARE RESULTING IN
MLCAPES AROUND 1000 J/KG...WITH ADDITIONAL SURFACE HEATING AIDING IN
FURTHER DESTABILIZATION. ELY SURFACE WINDS ACROSS MT BENEATH
INCREASING SWLY MID LEVEL FLOW WILL CONTINUE TO SUPPORT EFFECTIVE
BULK SHEAR VALUES OF 40-50 KT FOR SUPERCELLS. STORMS SHOULD
INCREASE IN INTENSITY AS THEY MOVE OFF THE HIGHER TERRAIN INTO THE
INSTABILITY AXIS. MAIN THREATS ARE EXPECTED TO BE HAIL AND DAMAGING
WIND GUSTS.
TSTMS ARE EXPECTED TO SPREAD EWD INTO ERN MT/NERN WY THIS EVENING
AND REACH WRN ND/NWRN SD LATER IN THE FORECAST PERIOD. THIS
ACTIVITY MAY EVOLVE INTO AN MCS GIVEN INCREASING LOW LEVEL WAA
EXPECTED TONIGHT ALONG THE NOSE OF STRENGTHENING/VEERING LLJ INTO
THE NRN HIGH PLAINS.
...WI/MN/SD/NEB...
SURFACE FRONT EXTENDED FROM NERN WI SWWD THROUGH MSP TO SERN SD AND
INTO THE NEB PANHANDLE...WITH THE ERN EXTENT EXPECTED TO CONTINUE
MOVING SWD AND REACHING SRN WI TO THE MN/IA BORDER BY 12Z SUNDAY.
AIR MASS ALONG THE PORTION OF THIS BOUNDARY IN MN TO SD AND NEB HAS
BECOME MODERATELY UNSTABLE. ALTHOUGH POTENTIAL FOR TSTM DEVELOPMENT
APPEARS LOW GIVEN RIDGING ALOFT...THE MODERATE INSTABILITY AND STEEP
LOW LEVEL LAPSE RATES WILL SUPPORT AN ISOLATED STRONG TO SEVERE
STORM WITH HAIL AND GUSTY WINDS.
...SW TX...
A MODERATELY UNSTABLE AIR MASS HAS DEVELOPED FROM CHIHUAHUA MEXICO
NWD THROUGH FAR W TX INTO ADJACENT PARTS OF SRN NM. GREATEST
POTENTIAL FOR ORGANIZED STORMS SHOULD BE CONFINED TO THE TX BIG BEND
REGION WHERE EFFECTIVE BULK SHEAR IS 30-40 KT. HOWEVER... MODELS
SUGGEST HIGHER LIKELIHOOD FOR TSTM DEVELOPMENT NORTH OF THE TX BIG
BEND AS CONFIRMED BY CURRENT LIGHTNING DATA AND REGIONAL RADARS.
ALTHOUGH DEEP LAYER SHEAR IS RATHER WEAK WITH NWD EXTENT...MODERATE
INSTABILITY AND STEEP LAPSE RATES SUPPORT MAINLY A THREAT FOR
ISOLATED HAIL.
...EXTREME SRN FL PENINSULA...
A FEW TSTMS HAVE DEVELOPED SO FAR ALONG THE SEA BREEZE BOUNDARY IN
BROWARD COUNTY. DIURNAL TSTM THREAT WILL CONTINUE ACROSS THE SRN FL
PENINSULA WHERE THE AIR MASS HAS BECOME MODERATELY UNSTABLE. ELY
LOW LEVEL WINDS LOCATED BENEATH WLY MID LEVEL WINDS SHOULD MAINTAIN
EFFECTIVE BULK SHEAR VALUES TO AROUND 30 KT...SUPPORTING AN ISOLATED
THREAT FOR STRONG GUSTY WINDS AND/OR HAIL WITH THE STRONGEST CORES.
..PETERS.. 05/19/2007
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